Toroidal coil assemblies, including toroidal inductors and toroidal transformers, are passive electronic components. A toroidal coil assembly typically includes a circular ring-shaped (toroidal) magnetic core of high magnetic permeability material, such as iron powder or ferrite. In at least one typical toroidal inductor, a wire is coiled around the toroidal core through the entire circumferential length thereof. Generally, for a toroidal transformer, a first wire (primary winding) is wrapped around a first half of the circumference of the core, and a second wire (secondary winding) is wrapped around the second half of the circumference of the core. In both transformer and inductor coil assemblies, the wire turns are electrically insulated from each other.
Toroidal coil assemblies have long been used in electronic applications. Small toroidal coil assemblies are sometimes embedded in printed circuit boards and in molded block components.